Cantilevered probe detector with piezoelectric element

ABSTRACT

A disclosed chemical detection system for detecting a target material, such as an explosive material, can include a cantilevered probe, a probe heater coupled to the cantilevered probe, and a piezoelectric element disposed on the cantilevered probe. The piezoelectric element can be configured as a detector and/or an actuator. Detection can include, for example, detecting a movement of the cantilevered probe or a property of the cantilevered probe. The movement or a change in the property of the cantilevered probe can occur, for example, by adsorption of the target material, desorption of the target material, reaction of the target material and/or phase change of the target material. Examples of detectable movements and properties include temperature shifts, impedance shifts, and resonant frequency shifts of the cantilevered probe. The overall chemical detection system can be incorporated, for example, into a handheld explosive material detection system.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of the earlier filing date of U.S.Provisional Application No. 60/614,592, filed Oct. 1, 2004, which ishereby incorporated by reference in its entirety.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under Prime Contract No.DE-AC05-00OR22725 awarded to UT-Battelle, LLC, by the U.S. Department ofEnergy and a subcontract awarded to the University of Nevada, Reno byUT-Battelle, LLC. The Government may have certain rights in thisinvention.

FIELD

This disclosure relates generally to chemical detection, and moreparticularly to systems and methods for sensing target materials, suchas explosive materials, using cantilevered probes.

BACKGROUND

The burgeoning market for explosives screening equipment and an increasein research on chemical and explosive detection technologies are inresponse to the greater need to perform real-time detection ofundesirable chemicals and hidden explosives, such as those concealed inluggage, shipping containers, land mines, and unexploded ordinances. Themarket for devices that screen people for explosives and various typesof biological, chemical or nuclear/radiological weapons is estimated byHomeland Security Research Corp. to reach $3.5 billion by 2006 and $9.9billion by 2010.

Among the wide range of materials from which explosives can be made areorganic nitrates, organonitro compounds, ketone and acyl peroxides,inorganic chlorates, perchlorates, nitrates, fulminates, and acetylides.Some of the explosive residue chemical compounds for detection andidentification include 2,4,6-trinitrotoluene (TNT),2,4,6,n-tetranitro-n-methylaniline (Tetryl),1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), pentaerythritoltetranitrate (PETN), glycerol trinitrate (nitroglycerin), and ethyleneglycol dinitrate (EGDN).

Many obstacles remain for scientists and engineers working to developequipment and processes for detecting explosives. Dogs continue to bethe preferred explosive detectors, yet widespread deployment of canineteams is neither practical nor cost effective. Moreover, currentlyavailable non-canine explosive sensor equipment tends to be complex,bulky, and expensive, and cannot be miniaturized easily.

Currently available explosive and bomb detection systems typicallyabsorb particulate or vapor matter onto a surface, and analyze thematter using techniques such as ion mobility spectrometry (IMS), massspectroscopy, nuclear magnetic resonance analysis, and gaschromatography. Successful explosive and chemical detection techniquescan require sensitivity as low as parts per trillion to parts perquadrillion, in that small explosive devices such as anti-personnel landmines may be constructed from plastic and other non-metallic substanceshaving low vapor pressures. One exemplary explosive and chemicaldetection system used in airports exposes luggage to a stream of airthat dislodges chemicals into the air as vapors, which are subsequentlyconcentrated to create detectable levels of the chemicals.Unfortunately, many conventional explosive and chemical detectionsystems still have high false alarm rates, slow throughput, operatordependences, and high transaction costs.

Some conventional explosive detection systems include cantileveredelements. One example of this type of system is described by Thundat in“Microcantilever Detector for Explosives,” U.S. Pat. No. 5,918,263,issued Jun. 29, 1999 (Thundat). As disclosed in Thundat, explosive gasmolecules that have been adsorbed onto a microcantilever aresubsequently heated to cause combustion, which in turn causes bendingand a transient resonance response of the microcantilever. Movement ofthe microcantilever is detected by a laser diode, which is focused onthe microcantilever, and a photodetector, which detects deflection ofthe reflected laser beam caused by a heat-induced deflection andresonance response of the microcantilever. Conventional explosivedetectors that include cantilevered elements, such as the detectordisclosed in Thundat, have a variety of limitations. For example, manysuch detectors cannot be miniaturized because they require externalcantilever actuation and external sensing.

SUMMARY

Disclosed herein are embodiments of a chemical detection system fordetecting a target material, such as an explosive material. Some ofthese embodiments have potential as extremely sensitive yet inexpensivesensors that can be mass-produced, thereby enabling large-scale sensordeployment. For example, some embodiments may offer several orders ofmagnitude greater sensitivities when compared to othermicro-electrical-mechanical systems (MEMS) such as quartz crystalmicrobalances (QCM), flexural plate wave oscillators (FPW), and surfaceacoustic wave devices (SAW).

Embodiments of the disclosed chemical detection system can include, forexample, a cantilevered probe, a probe heater thermally coupled to thecantilevered probe, and a piezoelectric element disposed on thecantilevered probe. The piezoelectric element can be configured todetect the target material by a variety of processes, such as bydetecting bending, vibrations, recoil, or other movements of thecantilevered probe, a temperature change of the cantilevered probe, animpedance shift of the cantilevered probe, or a resonant frequency shiftof the cantilevered probe. In some embodiments, the piezoelectricelement is configured to actuate movement of the cantilevered probe.This movement can be useful in the detection process, such as to detecta resonant frequency shift of the cantilevered probe.

The piezoelectric element can include a piezoelectric film disposed on asurface of the cantilevered probe. In some embodiments, thepiezoelectric element comprises zinc oxide, lead zirconate titanate,aluminum nitride, a piezoelectric material, or a derivative orcombination thereof. The piezoelectric element also can comprise apyroelectric material. In some embodiments, the probe heater includespiezoresistive element formed in the cantilevered probe, a heaterelement disposed on the cantilevered probe, or both.

Embodiments of the disclosed chemical detection system can include avariety of additional elements. Some embodiments include an interfacecircuit electrically coupled to the piezoelectric element. For example,some embodiments include an interface circuit comprising thepiezoelectric element as a bridge element in an AC bridge circuit. ThisAC bridge can be tuned, for example, to one of an on-resonance conditionor an off-resonance condition to detect the target material. Embodimentsof the disclosed chemical detection system also can include a thermallyconductive mesh substantially surrounding the cantilevered probe. Thiscan be useful, for example, to limit the egression of thermal energyliberated by exothermic reactions, such as the deflagration of explosivematerials. Embodiments of the disclosed chemical detection system alsocan include a mechanical stop configured to contact the cantileveredprobe. This stop can be used, for example, to detect movement of thecantilevered probe. Some embodiments are handheld. These and otherembodiments can include an enclosure, such as a handheld enclosure.

Examples of target materials that can be detected by some embodiments ofthe disclosed chemical detection system include 2,4,6-trinitrotoluene,2,4,6,n-tetranitro-n-methylaniline,1,3,5-trinitro-1,3,5-triazacyclohexane,1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane, pentaerythritoltetranitrate, glycerol trinitrate, ethylene glycol dinitrate, andderivatives and combinations thereof. To aid in the detection of traceconcentrations, some embodiments include a target material concentratorcoupled to the cantilevered probe. These and other embodiments also caninclude a selective coating disposed on at least a portion of thecantilevered probe, the selective coating being configured for selectiveadsorption of the target material. In these and other embodiments,additional selectivity can be achieved by fabricating multiplecantilevered probes in a cantilevered probe array. In these arrays, atleast two of the cantilevered probes can be frequency-differentiated.For example, at least one cantilevered probe can be tuned to anon-resonance condition while at least one other cantilevered probe istuned to an off-resonance condition. Multiple cantilevered probes in acantilevered probe array, such as frequency-differentiated cantileveredprobes, can be connected in series.

Also disclosed are embodiments of a method of detecting a targetmaterial, such as an explosive material. These embodiments can include,for example, exposing a cantilevered probe to a carrier including atarget material such that the target material is transferred onto thecantilevered probe. Some embodiments also include heating thecantilevered probe, such as to a temperature sufficient to cause thetarget material to undergo a phase change or to a temperature sufficientto cause the target material to deflagrate or ignite. These and otherembodiments also can include piezoelectrically detecting a movement ofthe cantilevered probe or a property of the cantilevered probe, such asby generating an electrical signal with a piezoelectric elementconnected to the cantilevered probe. The same or another piezoelectricelement also can be used to piezoelectrically actuate a movement of thecantilevered probe. In some embodiments, piezoelectric elements aredriven by a variable-frequency drive voltage, such as to isolate theresponses of frequency-differentiated cantilevered probes.

In some disclosed embodiments, the movement of the cantilevered probe ora change in the property of the cantilevered probe is caused bytransferring the target material onto the cantilevered probe. Somedisclosed embodiments also include causing the target material toundergo a phase change or a reaction. This phase change or reaction alsocan cause the movement of the cantilevered probe or a change in theproperty of the cantilevered probe. Also among the movements andproperty changes that can be piezoelectrically detected are resonantfrequency shifts, cantilever bending, thermal signatures, recoilresponses, pyroelectric charge generation, impedance shifts andtemperature shifts. Based on the movement of the cantilevered probe or achange in the property of the cantilevered probe, some embodiments alsoinclude identifying the target material. Identifying the target materialcan involve comparing a cantilevered probe response to a referencecantilevered probe response.

Also disclosed are embodiments of a method for making a chemicaldetection system. These embodiments can include providing a cantileveredprobe, providing a probe heater thermally coupled to the cantileveredprobe, and providing a piezoelectric element disposed on thecantilevered probe. In some of these embodiments, providing thepiezoelectric element includes depositing a piezoelectric film on asurface of the cantilevered probe. These and other embodiments also caninclude depositing a selective coating on a surface of the cantileveredprobe. More than one cantilevered probe can be assembled to form acantilevered probe array.

Various embodiments are illustrated in part by the accompanying drawingsand the detailed description given below. The drawings and the detaileddescription should not be taken to limit the invention to the specificembodiments, but are for explanation and understanding. Furthermore, thedrawings are not drawn to scale. The drawings and the detaileddescription are merely illustrative of the invention rather thanlimiting, the scope of the invention being defined by the appendedclaims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a chemical detection system fordetecting at least one explosive material, in accordance with someembodiments of the current invention;

FIG. 2 is a perspective view of a self-sensed cantilevered probe array,in accordance with some embodiments of the current invention;

FIG. 3 is a plan view of a pair of cantilevered probes with probeheaters and piezoelectric detectors, in accordance with some embodimentsof the current invention;

FIG. 4 is a schematic diagram of a system for detecting an explosivematerial, in accordance with some embodiments of the current invention;

FIG. 5 a, FIG. 5 b and FIG. 5 c are graphs showing characteristicresonant frequencies of a cantilevered probe prior to exposure to anexplosive material, after exposure to the explosive material, and afterdeflagration or ignition of the explosive material, respectively, inaccordance with some embodiments of the current invention;

FIG. 6 a, FIG. 6 b and FIG. 6 c are elevation views showingcharacteristic bending of a cantilevered probe prior to exposure to anexplosive material, after exposure to the explosive material, and afterdeflagration or ignition of the explosive material, respectively, inaccordance with some embodiments of the current invention;

FIG. 7 a, FIG. 7 b and FIG. 7 c are elevation views showing bending andvibrations of a cantilevered probe prior to exposure to an explosivematerial, after exposure to the explosive material, and afterdeflagration or ignition of the explosive material, respectively, inaccordance with some embodiments of the current invention;

FIG. 8 a, FIG. 8 b and FIG. 8 c are graphs showing periodic heating of acantilevered probe prior to exposure to an explosive material, duringexposure to the explosive material, and after deflagration or ignitionof the explosive material, respectively, along with a generatedpiezoelectric detector output signal, in accordance with someembodiments of the current invention;

FIG. 9 is a plan view of an array of cantilevered probes with anexplosive material concentrator surrounding the cantilevered probearray, in accordance with some embodiments of the current invention;

FIG. 10 is a perspective view of a handheld system for detecting anexplosive material, in accordance with some embodiments of the currentinvention; and

FIG. 11 is a flow chart of a method for detecting an explosive material,in accordance with some embodiments of the current invention.

DETAILED DESCRIPTION

The following terms may be abbreviated in this disclosure:1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX),1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),2,4,6,n-tetranitro-n-methylaniline (Tetryl), 2,4,6-trinitrotoluene(TNT), atomic force microscopy (AFM), central processing unit (CPU),deep reactive ion etching (D-RIE), digital signal processor (DSP),ethylene glycol dinitrate (EGDN), field-programmable gate array (FPGA),flexural plate wave oscillators (FPW), fast Fourier transform (FFT),glycerol trinitrate (nitroglycerin), ion mobility spectrometry (IMS),lead zircanate titinate (PZT), local area network (LAN),micro-electrical-mechanical systems (MEMS), pentaerythritol tetranitrate(PETN), quality (O), quartz crystal microbalances (QCM),silicon-on-insulator (SOI), surface acoustic wave devices (SAW),universal serial bus (USB), and wide area network (WAN).

Unless otherwise explained, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this disclosure belongs. The singular terms“a,” “an,” and “the” include plural referents unless context clearlyindicates otherwise. Similarly, the word “or” is intended to include“and” unless the context clearly indicates otherwise. The terms“comprises” and “includes” are equivalent. The same reference numeralsare used throughout the Figures to indicate similar or identicalfeatures. U.S. application Ser. No. 10/967,748 is incorporated herein byreference.

Disclosed herein are embodiments of a chemical sensor, embodiments of amethod for making the disclosed chemical sensor and embodiments of amethod for sensing chemicals. Although not limited by any particularadvantages, the disclosed embodiments may have one or more advantagesover the prior art. Some disclosed embodiments require detection surfaceareas that are orders of magnitude smaller than the surface areasrequired by other types of sensors. In addition, some embodiments arecapable of operating in several detection modes, such as mass loadingand bending. Most other sensors operate in only a single detection mode.Furthermore, many of the disclosed embodiments can be mass-produced atrelatively low cost. For example, silicon cantilevered probes can bemanufactured using standard semiconductor manufacturing equipment.Finally, some of the disclosed embodiments have demonstrated superiordetection sensitivities in comparison to at least some conventionalsensors.

FIG. 1 illustrates a chemical detection system 10 for detecting one ormore explosive materials 16 or other target chemical species 12 alsoreferred to as target materials, in accordance with some embodiments ofthe present invention. As shown, the chemical detection system 10includes a cantilevered probe 30, a probe heater 36 thermally coupled tothe cantilevered probe 30, and a piezoelectric element 32 disposed onthe cantilevered probe 30. The piezoelectric element 32 can beconfigured to detect explosive material 16 adsorbed onto thecantilevered probe 30, such as when the probe heater 36 heats thecantilevered probe 30. In various embodiments, the piezoelectric element32 can provide a piezoelectric element output signal related to, forexample, a resonant frequency shift, cantilever bending, a thermalsignature, a recoil response, a pyroelectric charge generation, animpedance shift, a temperature shift, or combinations thereof.Throughout this disclosure, descriptions of the adsorption of explosivematerial 16 or other target chemical species 12 refer to the attachmentor inclusion of such material onto or into the cantilevered probe 30,whether by adsorption, absorption, reaction, or any other form ofattachment or incorporation.

The explosive material 16 can include, for example,2,4,6-trinitrotoluene (TNT), 2,4,6,n-tetranitro-n-methylaniline(Tetryl), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), pentaerythritoltetranitrate (PETN), glycerol trinitrate (nitroglycerin), ethyleneglycol dinitrate (EGDN), derivatives thereof, or combinations thereof.

The cantilevered probes 30 can be self-sensing. The chemical detectionsystem 10 can include multiple cantilevered probes 30 arranged in acantilevered probe array 20. Each cantilevered probe 30 can have one ormore suspended cantilevered element and one or more associatedpiezoelectric element 32. The piezoelectric element 32 can include, forexample, a deposited layer of piezoelectric material, such as zinc oxide(ZnO), lead zircanate titinate (PZT), aluminum nitride, a piezoelectricmaterial, or a derivative or combination thereof. The piezoelectricelement 32 also can include a pyroelectric material. The piezoelectricelement 32 can be configured to bend, deflect or vibrate thecantilevered element when excited or actuated by an applied drivevoltage. The piezoelectric element 32 also can be configured to generatea voltage as the associated cantilevered probe 30 bends, deflects orvibrates. In this way, the piezoelectric element 32 can be configured tosense movements of the associated cantilevered probe 30 such as shiftsin bending, vibrations, or recoil and/or to actuate movement of theassociated cantilevered probe 30. Some embodiments, however, include aseparate piezoelectric drive mechanism or other mechanism that drivesthe cantilevered probe 30.

As mentioned above, the cantilevered probe 30 may be part of acantilevered probe array 20. The cantilevered probes 30 in thecantilevered probe array 20 may be frequency-differentiated such thatcantilevered probes having different effective masses or effectivespring constants exhibit different resonant frequencies. Thecantilevered probes 30 can be manufactured, for example, with smalldifferences in cantilever lengths, resulting in separations in resonantfrequencies that allow the resonant frequency of each cantilevered probein the cantilevered probe array 20 to be detected with as few as twowires connected to the cantilevered probe array 20. Thus, thecantilevered probe arrays 20 with two or more cantilevered probes 30 canbe packaged and connected to an interface circuit 40 with a minimalnumber of bond pads, interconnection traces and bond wires to externalinterface and control electronics. The interface circuit 40, which canbe coupled to the cantilevered probe array 20, can be configured toactuate and sense movement of the cantilevered probes 30. Parallelarrays of cantilevered probes 30 can be configured with elements thatnumber from a few to a million or more cantilevered probes on onesubstrate or die. Groups of cantilevered probe arrays 20 may beconnected, for example, during on-chip trace definition, while beingwire-bonded to a leadframe or package, or at the socket or board level.

Non-overlapping, independent and orthogonal explosive andchemical-sensing effects on individual cantilevered probes 30 in thecantilevered probe array 20 may be desirable but not necessary when manycantilevered probes 30 with various coatings and coating thicknesses areused for detection. Signal processing and pattern recognition of theresonance-frequency data from multiple cantilevered probes 30 may beemployed to differentiate between various explosive materials andchemicals in varying concentrations having sometimes small and sometimesnull effects. Differentiation between similar chemical substances can bemade, and their constituency and concentration can be determined, in asystem where a variety of selective coatings 34 are applied to multiplecantilevered probes 30. These selective coatings 34, for example, can beused to selectively adsorb different types of chemicals-onto thecantilevered probes 30. The selective coating 34 can be positioned on oraround one or more of the cantilevered probes 30 of a cantilevered probearray 20, such as one or more cantilevered probes 30 with or withoutprobe heaters 36, to provide, for example, two or more differentiableoutput signals for identifying the target chemical species 12.

The chemical detection system 10 can be configured to detect one or moretarget chemical species 12, such as mercury, hydrogen, an alcohol, watervapor, an explosive material, a chemical element, a chemical compound,an organic material, an inorganic material, a gaseous substance, aliquid, a biological material, a DNA strand, a bioactive agent, a toxin,or derivatives or combinations thereof. Throughout this disclosure, thetarget chemical species 12 can be any chemical, biological, or explosivematerial targeted for detection.

Typically, one or more cantilevered probes 30 can be configured torespond when exposed to the explosive material 16. For example, thecantilevered probes 30 may respond when absorbing, adsorbing, orotherwise reacting to the explosive material 16 and/or other targetchemical species 12. When the cantilevered probe array 20 is exposed tothe explosive material 16 and is actuated by the interface circuit 40,one or more of the cantilevered probes 30 in the cantilevered probearray 20 may exhibit a response, such as a shift in bending, a change ina resonant frequency, an impedance shift, or a shift in temperature.When exposed to the explosive material 16 or other target chemicalspecies 12, the cantilevered probes 30 also may increase or decrease inmass, or become more or less rigid. These and other responses may resultin the generation of a piezoelectric element output signal.

In one example, the cantilevered probe 30 comprises a patterned layer ofgold. When exposed to mercury, the gold and mercury react to form anamalgam. The gold-mercury amalgam adds mass to the cantilevered probe 30and therefore tends to decrease the resonant frequency of thecantilevered probe 30. Amalgam formation, however, also increases themechanical stiffness of the cantilevered probe 30, thereby increasingits natural resonant frequency. These two effects tend to cancel eachother, though one effect can be made dominant by careful selection andplacement of a chemical-sensitive selective coating 34 on thecantilevered probe 30.

In one exemplary detection mode, the adsorbed explosive material 16deflagrates or ignites when heated by a probe heater 36 to cause anexothermic reaction, which in turn causes a piezoelectric output signalto be generated by a piezoelectric element 32. For example, thepiezoelectric element 32 may generate an electrical charge when theprobe heater 36 heats the cantilevered probe 30. The piezoelectricelement 32 also may detect an increase in temperature of thecantilevered probe 30 when the exothermic reaction occurs.Alternatively, the explosive material 16 may melt or evaporate when theprobe heater 36 heats the cantilevered probe 30 and the phasetransformation may be detected with the piezoelectric element 32.Alternatively, the explosive material 16 may be detected by an impedanceshift of the piezoelectric element 32 when the probe heater 36 heats thecantilevered probe 30. The reactive portion, the resistive portion or acombination of both may shift in response to heating of the cantileveredprobe 30.

In some embodiments, the piezoelectric characteristics of thepiezoelectric element 32 may detect a shift in bending of thecantilevered probe 30 as the explosive material 16 is adsorbed onto asurface of the cantilevered probe 30, is desorbed from the cantileveredprobe 30, or reacts exothermically on the cantilevered probe 30. Forexample, as the explosive material 16 accumulates on the cantileveredprobe 30, the cantilevered probe 30 may bend upwards or downwardsdepending on the stress state of the added or removed material.Alternatively or in conjunction, the piezoelectric element 32 may detecta shift in a resonant frequency of the cantilevered probe 30 when theexplosive material 16 is adsorbed onto the cantilevered probe 30, isdesorbed from the cantilevered probe 30, or reacts exothermally on thecantilevered probe 30. For example, as the explosive material 16accumulates on the cantilevered probe 30, the resonant frequency maydecrease due to the additional mass loading. Similarly, as the explosivematerial 16 desorbs or is otherwise removed, the resonant frequency mayreturn towards its previous condition prior to mass loading. The effectsdescribed above may occur in various combinations. Analysis of one or amultiplicity of these effects may be used to identify an explosive or anon-explosive material absorbed onto cantilevered probe 30.

The probe heater 36, a piezoresistor serving as a temperature sensor,the piezoelectric element 32, or another on-board temperature sensor maybe used to indicate the temperature of the cantilevered probe 30, fromwhich the ignition temperature or deflagration temperature of theexplosive material 16 may be determined. Alternatively, an onboardtemperature sensor may be used to determine the heat of vaporization,melting temperature, phase change, chemical reactions, exothermicreactions, endothermic reactions, or time dependencies thereofassociated with the explosive material 16 or other target chemicalspecies 12 to aid in the identification.

As discussed above, one or more selective coatings 34 may be disposed onone or more cantilevered probes 30 in the cantilevered probe array 20 tofacilitate chemical detection and specificity. For example, one or morecantilevered probes 30 in the cantilevered probe array 20 may be coated,uncoated, or otherwise treated to detect the explosive material 16. Theselective coating 34 may be applied to a portion of one or more of thecantilevered probes 30 in the cantilevered probe array 20. For example,the selective coating 34 may be applied to the topside or bottom side ofone or more of the cantilevered probes 30 or to portions thereof. Theselective coating 34 can include, for example, an epoxy resin such asNovolac™, a fluoropolymer such as FluoroPel™, a gold layer, a palladiumlayer, an alcohol-absorbent polymer, a water-absorbent material, achemical-sensitive polymer, a chemical-sensitive layer, a biosensitivematerial, a thiol, or derivatives or combinations thereof.

Various application methods can be used to deposit or apply theselective coating 34 and to otherwise treat surfaces of the cantileveredprobes 30. The selective coatings 34 can comprise, for example, a dippedcoating, a sprayed coating, or a dispensed coating disposed on at leasta portion of one or more of the cantilevered probes 30. An exemplarychemical-sensitive selective coating 34 includes a masked coatingdisposed on a portion of one or more of the cantilevered probes 30. Inan alternative application method, a non-homogeneous coating material isapplied to a set of cantilevered probes 30 in the cantilevered probearray 20, such that constituents of the non-homogeneous coating materialare deposited on the cantilevered probes 30 with suitable variations incomposition, coverage, and/or thickness.

In some disclosed embodiments, the chemical detection system 10 includesone or more reference cantilevered probes 30 r in the cantilevered probearray 20. The reference cantilevered probe 30 r can provide a referencecantilevered probe response when the cantilevered probe array 20 isexposed to the explosive material 16 or other target chemical species12. The reference cantilevered probes 30 r can be formed, for example,with no coating materials disposed thereon to reduce or eliminatesensitivity to the explosive material 16 or other target chemicalspecies 12. Alternatively, the reference cantilevered probes 30 r canhave an inert coating disposed on their surface to reduce or eliminatesensitivity to the explosive material 16. Alternatively, one or morereference cantilevered probes 30 r can be mechanically isolated fromexposure to the explosive material 16 while other portions of thecantilevered probe array 20 are exposed.

The explosive material 16, which may be located in a liquid or gascarrier 14, such as air, water, low-pressure gas, or plasma, can betransported in a forced or free manner towards the cantilevered probes30. Once the explosive material 16 makes contact with surfaces of thecantilevered probes 30 it may invoke, for example, shifts in resonantfrequency, Q factor, impedance, phase, or deflection amplitudes.Impedance shifts may be obtained, for example, by absorbing explosivematerial 16 or other target chemical species 12 directly into the bulkof a piezoelectric or pyroelectric film of the piezoelectric element 32.The absorption may be enhanced, for example, by increasing the peripheryof unpassivated sidewalls, such as with narrow line widths and smallspaces between multiple segments of the piezoelectric element 32.

The cantilevered probe array 20 may be actuated with an excitationvoltage applied to a piezoelectric drive mechanism serving optionally asthe piezoelectric element 32 disposed on each of the cantilevered probes30 in the cantilevered probe array 20. To reduce the number of externalpads and connections, a group of cantilevered probes 30 may be connectedin series and electrically connected to a pair of cantilevered probearray drive pads 24, which may be electrically connected to an interfacecircuit 40. While this configuration can increase the series resistanceof the string, differentiation of individual cantilevered probes 30 maybe made by detection of signals at or near the resonant frequency of theselected cantilevered probes 30. Alternatively, a group of cantileveredprobes 30 may be connected in parallel and electrically connected to apair of cantilevered probe array drive pads 24, increasing the effectivecapacitance and decreasing the effective resistance, while stillallowing differentiation of individual cantilevered probe responsesbased on frequency. Alternatively, cantilevered probes 30 may beconnected in a network of series-connected and parallel-connectedcantilevered probes with frequency-identifiable addressable elements.

The interface circuit 40 can provide excitation voltages forpiezoelectric material on the cantilevered probes 30 and sensedeflections and vibrations of the cantilevered probes 30 with the sameor a different piezoelectric material. In one example, the interfacecircuit 40 includes an adjustable frequency generator that is scannedthrough a predetermined frequency range to excite one or more of thecantilevered probes 30 in the cantilevered probe array 20. In anotherexample, the interface circuit 40 includes an impedance analyzer that isscanned through a resonant frequency of at least one cantilevered probe30, measuring the magnitude and phase from the cantilevered probes 30and monitoring for any variations in impedance as the cantileveredprobes 30 are exposed to one or more explosive materials 16. In anotherexample, the interface circuit 40 includes an oscillator circuitoperating at a resonant frequency of at least one cantilevered probe 30in the cantilevered probe array 20.

In another example, the interface circuit 40 includes an oscillatorcircuit operating at a predetermined frequency that is near, yetoff-resonance with respect to one or more of the cantilevered probes 30in the cantilevered probe array 20. This configuration may result in thegeneration of higher amplitudes of vibration and therefore higher outputsignals as the resonant frequency of the selected cantilevered probe 30shifts and moves towards the predetermined frequency. The predeterminedfrequency may be set, for example, slightly above or slightly below theresonant frequency of one or more of cantilevered probes 30.

In another example, the amplitude of bending and/or vibration ismonitored as the cantilevered probe 30 strikes against a fixed oradjustable mechanical stop such as a piezoelectric slab or a piezotube.In another example, the interface circuit 40 includes an impulse circuitfor applying an electrical impulse to the cantilevered probe array 20,and the ring-down of the cantilevered probes 30 is monitored. In anotherexample, noise, such as pink noise or white noise, is applied to excitethe cantilevered probe array 20. In some embodiments, the interfacecircuit 40 includes a network analyzer for detecting signals from thecantilevered probe array 20. The interface circuit 40 or a controller 50may include a fast Fourier transform generator to perform a fast Fouriertransform (FFT) on the shifted cantilevered probe response, and toprovide respective frequencies of the cantilevered probes 30 in thecantilevered probe array 20, which can be correlated with previouslymeasured probe responses and used to identify the explosive material 16and/or other target chemical species 12.

As discussed above, the chemical detection system 10 may include aninterface circuit 40 electrically coupled to a piezoelectric element 32that enables the detection of an explosive material 16 and/or a targetchemical species 12. The interface circuit 40 may contain, for example,the piezoelectric element 32 as a bridge element in an AC bridgecircuit. The AC bridge circuit may be tuned to an on-resonance conditionor on off-resonance condition to detect the explosive material 16. Inoperation, the output of the AC bridge circuit may shift as the resonantfrequency of the cantilevered probe 30 moves off-resonance with theaddition or subtraction of mass. Alternatively, the output of the ACbridge circuit may shift as the resonant frequency of the cantileveredprobe 30 moves towards the off-resonance tuned condition. Off-resonancetuning can allow any signals generated by the piezoelectric element 32to be distinguished from any output due to vibrations of thecantilevered probe 30. In some embodiments, one or more of thecantilevered probes 30 in the cantilevered probe array 20 are tuned toan on-resonance condition, and one or more other cantilevered probes 30in the cantilevered probe array 20 are tuned to an off-resonancecondition to detect the explosive material 16.

The interface circuit 40 may detect shifted cantilevered probe responsesfrom one or more actuated cantilevered probes 30 in the cantileveredprobe array 20. Examples of shifted cantilevered probe responses includea shift in a resonant frequency of one or more of the cantileveredprobes 30, a shift in a quality (Q) factor of one or more of thecantilevered probes 30, a shift in impedance of one or more of thecantilevered probes 30, a shift in phase of one or more of thecantilevered probes 30, a shift in deflection amplitude of one or moreof the cantilevered probes 30, and combinations thereof. With exposureto the explosive material 16 or other target chemical species 12, one ormore cantilevered probes 30 in the cantilevered probe array 20 canexhibit shifts in various properties. Similarly, with exposure to morethan one explosive material 16 or other target chemical species 12, oneor more cantilevered probes 30 in the cantilevered probe array 20 mayexhibit shifts from which multiple explosive materials 16 and/or othertarget chemical species 12 can be determined.

A controller 50 such as a central processing unit (CPU), a digitalsignal processor (DSP), a microcontroller, or a field-programmable gatearray (FPGA) may be included in the chemical detection system 10 toexecute programmed code and provide monitoring, controlling andanalyzing functions. The controller 50 can be in electricalcommunication with the interface circuit 40 and may be located, forexample, on a substrate 22 along with the cantilevered probe array 20,within an enclosure 60 on the same circuit board or in the same packageas the cantilevered probe array 20, or located remotely with respect tothe enclosure 60. The controller 50 may internally contain the functionsand capabilities of the interface circuit 40. The controller 50 mayreceive shifted cantilevered probe responses from a set of one or moreof the cantilevered probes 30 in the cantilevered probe array 20.

The explosive material 16 and other target chemical species 12 may bedetermined based on the shifted cantilevered probe response using, forexample, an algebraic model that relates shifts in cantilevered proberesponses to explosive materials and concentration. Alternatively, theexplosive material 16 may be determined based on a comparison betweenthe shifted cantilevered probe responses and a reference set ofcantilevered probe responses. Such reference sets can be obtained byexposing the cantilevered probes 30 to controlled environments withknown explosive materials and concentrations during calibration at thefactory or on site. The controller 50 can determine one or moreexplosive material 16, for example, through pattern recognitiontechniques, statistical processes, or fuzzy logic with comparison to thereference set of cantilevered probe responses. The reference set ofcantilevered probe responses can comprise, for example, a learned setobtained from shifts in cantilevered probe responses by cantileveredprobes 30 that have been exposed to known explosive materials andconcentrations under controlled laboratory or factory environments.

In some embodiments, heating of select cantilevered probes 30 burns off,evaporates off, or otherwise cleans and resets the cantilevered probe 30to a nascent condition. In these and other embodiments, the probe heater36 may be coupled to at least one cantilevered probe 30 in thecantilevered probe array 20. The probe heater 36 may be formed, forexample, with a resistive layer disposed on the surface of or formedwithin the cantilevered probe 30, such as by ion implantation. Exemplaryprobe heaters 36, which may be connected in series or parallel orindividually connected, can be formed on one, several, or all of thecantilevered probes 30 within the cantilevered probe array 20. The probeheaters 36 also may be used to react the explosive material 16 on thecantilevered probe 30 by heating the probe to a predeterminedtemperature where the reaction can occur. Alternatively, the probeheaters 36 may be used to ignite or deflagrate condensate of explosivevapors on the cantilevered probes 30. The probe heater 36 can comprise,for example, a resistive or a piezoresistive element formed in one ormore of the cantilevered probes 30 or a heater element, such as apatterned metal film, disposed on a surface of the cantilevered probe30.

The piezoelectric element 32, which may also serve as a piezoelectricdrive mechanism, can comprise, for example, zinc oxide, lead zircanatetitanate, aluminum nitride, a piezoelectric material, or derivatives orcombinations thereof. The piezoelectric element 32 also can comprise apyroelectric material. Piezoelectric materials typically expand orcontract when driving voltages are applied, and conversely generate avoltage when stressed or compressed. Piezoelectric materials aregenerally pyroelectric, in that a pyroelectric charge, voltage orcurrent is generated when the material is heated. For example, thepiezoelectric element 32 may generate a piezoelectric element outputsignal when the explosive material 16 in proximity to the piezoelectricelement 32 ignites, deflagrates or otherwise generates heat. In someembodiments, the piezoelectric element 32 serves simultaneously as apiezoelectric thermal detector and a piezoelectric drive mechanism todrive and excite the cantilevered probe 30, such as into resonance. Inother embodiments, the piezoelectric element 32 is separated from apiezoelectric drive mechanism, such as a piezoelectric drive mechanismthat also is located on a surface of cantilevered probe 30.

The chemical detection system 10 may contain one or more cantileveredprobe arrays 20 in an enclosure 60, which may include an inlet port 62and an outlet port 64 for transport of the explosive material 16, thetarget chemical species 12, and the carrier 14. The explosive material16 may enter the enclosure 60 through the inlet port 62 and be exposedto the cantilevered probe array 20. The explosive material 16 orbyproducts thereof may exit through the outlet port 64. The enclosure 60also may include filters, scrubbers, and other media treatment elementsto aid in the detection of the explosive material 16.

A transport mechanism 66 such as a pump or a fan with ductwork or pipingmay be included for transporting the explosive material 16 to thecantilevered probe array 20. The chemical detection system 10 also mayinclude an explosive material concentrator 68 coupled to one or more ofthe cantilevered probes 30. The concentrator 68, such as a pressurizingsystem or a condenser and heater system, may be included to concentratethe explosive material 16 and/or other target chemical species 12proximal to the cantilevered probe array 20 to facilitate detection. Insome embodiments, the explosive material 16 is concentrated on one ormore cantilevered probes 30 when the concentrator 68 is locally heated.

The chemical detection system 10 may include a thermally conductive mesh58 such as a copper screen or a metal mesh substantially surrounding thecantilevered probes 30 to limit the egression of thermal energy, such asfrom an exothermic reaction. As the explosive material 16 deflagrates,ignites or otherwise burns, hot air may be generated near thecantilevered probe 30. The thermally conductive mesh 58 may facilitatecooling of the hot air and otherwise limit heat transfer away from thecantilevered probes 30, such as beyond the enclosure 60.

The chemical detection system 10 may be connected to a local areanetwork (LAN), a wide area network (WAN), the Internet, or othernetworked communication system via one or more wired or wirelessconnections. The chemical detection system 10 may be installed, forexample, into an air handling system of a building or airport that hasmany inlets, into a standalone unit with a portal for chemicaldetection, or into a handheld unit for portable use. Moreover, thechemical detection system 10 may be installed in shipping containers andcrates during storage and transit for chemical detection and monitoring.

FIG. 2 illustrates a self-sensed cantilevered probe array, in accordancewith some embodiments of the present invention. As shown, theself-sensed cantilevered probe array 20 includes a plurality ofcantilevered probes 30 on a substrate 22. The cantilevered probes 30 caninclude piezoelectric elements 32, probe heaters 36, and/orchemical-sensitive selective coatings 34. Variations in length orthickness of the cantilevered probes 30 and variations in the thicknessand coverage of the applied coatings may allow for frequencydifferentiation between the cantilevered probes 30 within thecantilevered probe array 20.

The cantilevered probes 30 may have a rectangular shape, though othershapes may be suitably used, such as pointed cantilevers, V-shapedcantilevers, triangular-shaped cantilevers, dual-arm cantilevers, orbalanced cantilevers. The cantilevered probes 30 may be arranged andattached to the substrate 22 in an array in which the cantileveredprobes are all identical, all different, or combinations thereof.

In some embodiments, the cantilevered probe array 20 is actuated with anexcitation voltage applied to a piezoelectric element 32 that serves asa piezoelectric drive mechanism and as a piezoelectric sense mechanism.In one example, the cantilevered probes 30 are series-connected to apair of cantilevered probe array drive pads 24 on the substrate 22. Thecantilevered probes 30 also can be parallel connected to the pair ofcantilevered probe array drive pads 24. The cantilevered probe array 20also can comprise a network of series-connected and parallel-connectedcantilevered probes that connect electrically to the pair ofcantilevered probe array drive pads 24. More than one group or array ofcantilevered probes 30 may be included on the substrate 22. Additionalconnections with associated pads may be made to the piezoelectricelements 32 on particular cantilevered probes 30. The substrate 22 alsomay have through-wafer vias for backside connection to the drive pads24.

The substrate 22 can include a semiconductor substrate such as a siliconwafer, a silicon-on-insulator (SOI) wafer, a glass substrate, or othersuitable substrate for forming the cantilevered probes 30 thereon. Thecantilevered probes 30 can comprise materials such as silicon,polysilicon, silicon nitride, zinc oxide, aluminum nitride, metals,pyroelectric materials, piezoelectric materials, or derivatives orcombinations thereof. These materials can be present in various forms,such as sheets, films and layers. For example, a zinc oxide, PZT oraluminum nitride film can be deposited on a layer of single-crystalsilicon, patterned, and etched. Conductive layers for top and bottomelectrodes, interconnections, and probe heater connections then can bedeposited and etched accordingly. The cantilevered probes 30 can bedefined with a photomask and associated lithographic sequences alongwith deep reactive ion etching (D-RIE) or anisotropic etching of thecantilevers and substrate. This allows the formation and freeing of thesilicon cantilevers with interconnected ZnO electrodes in series,parallel, or series-parallel configurations. Excitation and detection ofthe cantilevers can occur with voltages applied to the piezoelectricmaterial. The piezoelectric elements 32 may be formed with depositionand patterning processes as are known in the art. The probe heaters 36on the cantilevered probes 30 can be formed, for example, by selectivelyimplanting portions of the cantilevered probe 30 or by depositing,patterning and etching a metal film on the cantilevered probe 30.

A chemical-sensitive selective coating 34 may be applied to at least aportion of one or more of the cantilevered probes 30. Thechemical-sensitive coating 34 can include a material, such as an epoxyresin, a fluoropolymer, gold, palladium, an alcohol-absorbent polymer, awater-absorbent material, a chemical-sensitive polymer, achemical-sensitive material, a biosensitive material, a thiol, orderivatives or combinations thereof. The chemical-sensitive selectivecoating 34 may be applied, for example, with techniques such as dipping,spraying, or dispensing the coating on at least a portion of one or moreof the cantilevered probes 30. The chemical-sensitive coating materialmay be applied onto a portion of one or more of the cantilevered probes30 with the use of stencil masks or photomasks and photolithographicpatterning techniques. The chemical-sensitive selective coating 34 maybe applied in conjunction with photolithographic patterning, forexample, using standard sputtering and other deposition techniques knownin the art.

Multiple masking sequences can be used to apply multiple coatingmaterials. Alternatively, multiple-component chemical-sensitiveselective coatings 34 may be used. The multiple-componentchemical-sensitive selective coatings 34 can comprise, for example,non-homogeneous coating materials, which can be applied in such a waythat variations in coating thickness and/or composition occur when thematerials are deposited.

When exposed to the explosive material 16 or to the target chemicalspecies 12, one or more of the cantilevered probes 30 in thecantilevered probe array 20 may undergo an electrical or a mechanicalshift, such as a shifted resonant frequency, a shifted Q factor, ashifted impedance, a shifted phase, or a shifted deflection amplitude.The cantilevered probe array 20 may include one or more referencecantilevered probes 30 r to provide a reference cantilevered proberesponse when the cantilevered probe array 20 is exposed to theexplosive material 16 or to the target chemical species 12. Thereference cantilevered probes 30 r may be uncoated, coated with an inertmaterial, or otherwise protected from exposure to the explosive material16 and the target chemical species 12.

FIG. 3 is a plan view of a pair of cantilevered probes 30 with probeheaters 36 and piezoelectric elements 32 for detecting an explosivematerial, in accordance with some embodiments of the present invention.As shown, one or more probe heaters 36 are disposed on or formed in thecantilevered probes 30. The probe heater 36 heats the cantileveredprobes 30, for example, to initialize the cantilevered probes 30 priorto exposing the cantilevered probe array 20 to the explosive material.The probe heaters 36 also can be used to burn off, deflagrate, orotherwise react an explosive material that is adsorbed onto a surface ofthe cantilevered probe 30.

The piezoelectric elements 32, which may also serve as piezoelectricdrive mechanisms for the cantilevered probes 30, can be configured todetect an explosive material adsorbed onto the cantilevered probe 30when the cantilevered probe 30 is heated by the probe heater 36 tocause, for example, an exothermic reaction. In one example, thepiezoelectric element 32 generates a piezoelectric element output signalwhen the probe heater 36 heats the adsorbed explosive material and anexothermic reaction or a phase change occurs. In another example, thepiezoelectric element 32 detects an increase in temperature of thecantilevered probe 30 when an exothermic reaction occurs. In anotherexample, the piezoelectric element 32 detects a shift in bending of thecantilevered probe 30 when the explosive material is adsorbed onto thecantilevered probe 30, is desorbed from the cantilevered probe 30, orreacts exothermically on the cantilevered probe 30. In another example,the piezoelectric element 32 detects a shift in a resonant frequency ofthe cantilevered probe 30 when the explosive material is adsorbed, isdesorbed or exothermically reacts. In another example, the piezoelectricelement 32 detects an impedance shift when the explosive ornon-explosive material is adsorbed, is desorbed or exothermicallyreacts.

As show in FIG. 3, the cantilevered probe 30 can include a base end 26and a tip 28. The cantilevered probe array 20 may be attached to acommon base such as a substrate 22. The cantilevered probe 30 may have arectangular shape, although other shapes may be suitably used, such aspointed shapes, V-shapes, triangular-shapes, or dual-arm shapes. Atreated portion, such as the selective coating 34 disposed on at least aportion of the cantilevered probe 30, may aid in discriminating betweenvarious explosive materials and other target chemical species 12. Insome embodiments, the cantilevered probe 30 is attached at each end,with the center of the cantilevered probe 30 free to vibrate. In anotherembodiment, the cantilevered probe 30 is attached on all sides in adiaphragm or membrane configuration.

A drive mechanism, such as the piezoelectric element 32 serving as apiezoelectric drive mechanism or a separate piezoelectric drive element,can be coupled to the cantilevered probe 30. The piezoelectric element32 and/or the drive mechanism may comprise, for example, a patternedthin film of zinc oxide, PZT or aluminum nitride on a surface of thecantilevered probe 30. A sense mechanism may also be coupled to thecantilevered probe 30. The sense mechanism may comprise, for example, apiezoresistor attached to or formed in the cantilevered probe 30.

The probe heater 36 can be coupled to the cantilevered probe 30. Theprobe heater 36 can comprise, for example, a probe heater formed in oron the cantilevered probe 30. In addition to initiating an exothermicreaction or a phase change, the probe heater 36 may be used to heat thecantilevered probe 30 to an elevated temperature that initializes orre-initializes the treated portion or the selective coating 34.Alternatively, an external probe heater such as a heat lamp or a hot gassystem may be used to heat and re-initialize the cantilevered probe 30.Chemical re-initialization may be accomplished, for example, by usingcleaning processes or by reversing any chemical reactions that occurredon the treated portion.

Multiple cantilevered probes 30 may be arranged in a cantilevered probearray 20, the cantilevers being all identical, all different, or somecombination thereof. The cantilevered probes 30 of a cantilevered probearray 20 may be driven and sensed, for example, with a piezoelectricdrive element coupled to each cantilevered probe 30. In one embodiment,the piezoelectric elements in the array are connected in series. Theseries-connected piezoelectric elements in the array may be driven withas few as two electrical connections to the piezoelectric element array.Scanning the drive voltage through a range of frequencies can excite andsense one cantilevered probe 30 at a time, allowing interrogation of anycantilevered probe 30 in the array while minimizing the number ofelectrical connections required. In another configuration, thepiezoelectric elements in the array are connected in parallel, such thatas few as two electrical connections may be used to drive and sensecantilevered probes 30. In this configuration, failure of onecantilevered probe 30 does not prevent others from operating. In anotherconfiguration, the array of piezoelectric elements is connected in aseries-parallel arrangement.

FIG. 4 is a schematic diagram of a system for detecting an explosivematerial, in accordance with some embodiments of the present invention.As shown, the chemical detection system 10 includes one or morecantilevered probes 30, one or more probe heaters 36 thermally coupledto the cantilevered probes 30, and one or more piezoelectric elements 32disposed on the cantilevered probes 30. A controller 50 and an interfacecircuit 40 may be connected to one or more of the self-sensedcantilevered probes 30 configured in the self-sensed cantilevered probearray 20. The controller 50, which can be connected to the interfacecircuit 40, can be configured to drive and sense a plurality ofself-sensed cantilevered probes 30 in the cantilevered probe array 20.It should be observed that, in some embodiments, the cantilevered probearray 20 may be electrically connected to the interface circuit 40 withas few as two cantilevered probe array drive pads 24. At least onecantilevered probe 30 in the cantilevered probe array 20 may exhibit ashifted cantilevered probe response when the cantilevered probe array 20is exposed to an explosive material 16 or a target chemical species 12and the cantilevered probe array 20 is actuated by the interface circuit40. The piezoelectric element 32 can generate a piezoelectric elementoutput signal that may be analyzed by the controller 50.

The interface circuit 40 can be configured to actuate the cantileveredprobe array 20 with an excitation voltage applied to a piezoelectricmaterial such as piezoelectric element 32 disposed on each cantileveredprobe 30 in the cantilevered probe array 20. In one example, theinterface circuit 40 includes an adjustable frequency generator that isscanned through a predetermined frequency range. In another example, theinterface circuit 40 includes an impedance analyzer that is scannedthrough a resonant frequency of one or more cantilevered probes 30 inthe cantilevered probe array 20. In another example, the interfacecircuit 40 includes an oscillator circuit operating at a resonantfrequency of at least one cantilevered probe 30 in the cantileveredprobe array 20. In another example, the interface circuit 40 includes anoscillator circuit operating at a predetermined frequency that is set tobe off-resonance with respect to at least one cantilevered probe 30 inthe cantilevered probe array 20. In another example, the interfacecircuit 40 includes control circuitry to monitor the amplitude ofbending and vibration as the cantilevered probe 30 strikes against afixed or adjustable mechanical stop. In another example, the interfacecircuit 40 comprises an impulse circuit for applying an electricalimpulse to all of the cantilevered probes 30 in the cantilevered probearray 20. In another example, the interface circuit 40 or the controller50 includes a fast Fourier transform (FFT) generator to perform a fastFourier transform on the shifted cantilevered probe response. Theinterface circuit 40 can be configured to detect a shifted cantileveredprobe response from one or more actuated cantilevered probes 30, such asa shifted resonant frequency, a shifted Q factor, a shifted impedance, ashifted phase, or a shifted deflection amplitude.

The controller 50 may receive a shifted cantilevered probe response froma set of one or more cantilevered probes 30 in the cantilevered probearray 20. The explosive material 16 or other target chemical species 12may be determined, for example, based on the shifted cantilevered proberesponse. For example, the explosive material 16 may be determined basedon a comparison between the shifted cantilevered probe response and areference set of cantilevered probe responses. The reference set ofcantilevered probe responses can comprise, for example, a learned setobtained during the calibration of the chemical-sensing system or from astatistical database of cantilevered probe responses.

To cancel out common mode effects such as temperature, one cantileveredprobe 30 in the cantilevered probe array 20 may be a referencecantilevered probe 30 r, wherein the reference cantilevered probe 30 rprovides a reference cantilevered probe response when the cantileveredprobe array 20 is exposed to the explosive material 16 or the targetchemical species 12.

In some embodiments, the explosive material 16 and/or other targetchemical species 12 are adsorbed onto the cantilevered probe 30 byexposing the cantilevered probe 30 to an environment containing theexplosive material 16 and/or the other target chemical species 12. Toincrease the rate of adsorption, transport mechanisms and concentratorsmay be added to the chemical detection system 10.

Using heat generated by the onboard probe heater 36 or an external probeheater thermally coupled to the cantilevered probe 30, the adsorbedexplosive material 16 may ignite, deflagrate or otherwise burn. Thechemical detection system 10 may include a thermally conductive mesh 58substantially surrounding the cantilevered probes 30 to limit theegression of thermal energy from an exothermic reaction. A piezoelectricelement 32 disposed on the cantilevered probe 30 can generate, forexample, a piezoelectric element output signal when an exothermicreaction occurs. Alternatively or in addition, the piezoelectric element32 may also serve as a piezoelectric drive mechanism and a piezoelectricsense mechanism that senses the explosive material 16 by detectingbending or shifts in a resonant frequency of the cantilevered probe 30.

Detection of a non-explosive material or other target chemical species12 adsorbed onto a surface of the cantilevered probe 30 may beaccomplished, for example, using characteristic bending shifts,frequency shifts, exothermic or non-exothermic reaction indicators,phase change indicators, impedance shifts, or a combination thereof.Specificity and delineation of the explosive material 16 and othertarget chemical species 12 may be increased with selective coatingsapplied to one or more of the cantilevered probes 30 in the cantileveredprobe array 20.

FIG. 5 a, FIG. 5 b and FIG. 5 c show characteristic resonant frequenciesof a cantilevered probe prior to exposure to an explosive material,after exposure to the explosive material, and after deflagration,ignition, or evaporation of the explosive material, respectively, inaccordance with some embodiments of the present invention. An exemplaryresponse of a cantilevered probe with resonant frequency 90 a is seen inFIG. 5 a. As the explosive material is adsorbed onto the cantileveredprobe, the resonant frequency decreases with mass loading indicated byshifted resonant frequency 90 b, as seen in FIG. 5 b. After theexplosive material deflagrates, ignites, or otherwise desorbs from thecantilevered probe, the response curve with resonant frequency 90 creturns towards the resonant frequency 90 a, as seen in FIG. 5 c. Timedependencies of the frequency shifts prior to, during, or aftercantilevered probe heating may provide characteristics associated withvarious absorbed and desorbed explosive and non-explosive materials.Frequency shifts with the application of predetermined cantileverheating profiles may also provide characteristic signatures for theadsorbed materials.

FIG. 6 a, FIG. 6 b and FIG. 6 c show characteristic bending of acantilevered probe prior to exposure to an explosive material, afterexposure to the explosive material, and after deflagration or ignitionof the explosive material, respectively, in accordance with someembodiments of the present invention. In some embodiments, thecantilevered probe 30 initially has a tip 28 that is essentiallystraight, as seen in FIG. 6 a. With exposure to and adsorption of theexplosive material 16 or other target chemical species 12 onto a surfaceof the cantilevered probe 30, the probe may remain neutral, bendupwards, or bend downwards depending on the stress state of thecantilevered probe 30, with the tip 28 deflecting an amount equal to adisplacement 92 b, as seen in FIG. 6 b. When the cantilevered probe 30is heated with an onboard or external probe heater, the explosivematerial 16 may deflagrate, ignite, or otherwise desorb from the surfaceof the cantilevered probe 30, allowing the cantilevered probe 30 toreturn towards the initial, undeflected state with the tip 28 back in aneutral position, as seen in FIG. 6 c. It should be noted that localizedheating of the cantilevered probe 30 may contribute to beam bending, asthermal gradients across the cantilever produce moments that can causebending.

FIG. 7 a, FIG. 7 b and FIG. 7 c illustrate simultaneous bending andvibration of a cantilevered probe prior to exposure to an explosivematerial, after exposure to the explosive material, and afterdeflagration or ignition of the explosive material, respectively, inaccordance with some embodiments of the present invention. Thecantilevered probe 30 vibrates at resonant frequency 90 a about aneutral position prior to mass loading, as seen in FIG. 7 a. With theaddition of explosive material on the cantilevered probe 30, the tip maydeflect an average amount equal to a displacement 92 b while vibratingat a shifted or unshifted resonant frequency 90 b, as seen in FIG. 7 b.After deflagration, ignition, or desorption of the explosive materialfrom the cantilevered probe 30, the tip may return towards the initial,undeflected state while vibrating at a resonant frequency 90 c, as seenin FIG. 7 c.

FIG. 8 a, FIG. 8 b and FIG. 8 c illustrate periodic heating of acantilevered probe prior to exposure to an explosive material, duringexposure to the explosive material, and after deflagration or ignitionof the explosive material, respectively, along with a generatedpiezoelectric element output signal, in accordance with some embodimentsof the present invention. A piezoelectric element may generate arelatively small peak during each periodic heating cycle 94 a of thecantilevered probe and return to a low level as the cantilevered probecools, as indicated by the piezoelectric element output signal 96 a inFIG. 8 a. As the explosive material deposits and is adsorbed onto thecantilevered probe, the piezoelectric element output signal 96 areplicates relatively small peaks during each periodic heating cycle 94b, until sufficient explosive material is adsorbed so that the explosivematerial deflagrates and ignites or otherwise combusts, therebygenerating a high-level piezoelectric element output signal 96 bcorresponding to the energy released by the exothermic reaction, as seenin FIG. 8 b. Other mechanisms such as melting or evaporation may providepiezoelectric element output signals 96 b with higher, lower, ortime-dependent characteristics different from that shown. As thecantilevered probe cools down from the energy release, the piezoelectricelement output signal 96 c generally decreases towards a baseline withrelatively small peaks coinciding with periodic heating cycles 94 capplied to the cantilevered probe, as indicated in FIG. 8 c. Heat pulsesof the periodic heating cycles may be tailored, for example, to allowthe cantilevered probe to reach characteristic melting, evaporation, anddeflagration temperatures associated with a given explosive material.

FIG. 9 illustrates an array of cantilevered probes with an explosivematerial concentrator surrounding the cantilevered probe array, inaccordance with some embodiments of the present invention. One or moreselective coatings 34 are optionally applied to the cantilevered probearray 20 having a plurality of self-sensed cantilevered probes 30. Inthe example shown, the cantilevered probes 30 a, 30 b, 30 n areselectively coated with selective coatings 34 a, 34 b, 34 n,respectively. The reference cantilevered probe 30 r is shown with nocoating.

In this example, the cantilevered probes 30 a, 30 b, 30 n are nominallythe same size and thickness. Frequency differentiation for this set ofcantilevered probes can be achieved by varying the area of thecantilevered probes that is covered by the coating. Different amounts ofselective coating material can be disposed on each cantilevered probe,varying the effective mass of each cantilevered probe and changing theresonant frequencies accordingly. Piezoelectric elements 32 a, 32 b, 32n and probe heaters 36 a, 36 b, 36 n on the cantilevered probes 30 a, 30b, 30 n and 30 r, respectively, may be coated, partially coated, oruncoated with the selective coatings 34.

An explosive material concentrator 68 can be coupled to one or morecantilevered probes 30. The concentrator 68, such as a condenser andheater system, may be included to concentrate the explosive materialand/or other target chemical species 12 proximal to the cantileveredprobe array 20 for detection. In some embodiments, the concentrator 68with one or more heaters 68 a, 68 b, 68 c and 68 d surrounding thecantilevered probe array 20 is heated after the explosive material isadsorbed thereon, increasing the concentration of the explosive materialin the vicinity of the cantilevered probes 30 and allowing a higheradsorption rate of the explosive material onto one or more of thecantilevered probes 30. The heaters 68 a, 68 b, 68 c and 68 d thatsurround the cantilevered probe array 20 can comprise, for example,discrete heaters, integrated resistive heaters, or integrated circuitry.

FIG. 10 illustrates a handheld system for detecting an explosivematerial, in accordance with some embodiments of the present invention.As shown, the handheld system 70 includes an enclosure 60, one or morecantilevered probes 30 within the enclosure 60, probe heaters 36thermally coupled to the cantilevered probes 30, and piezoelectricelements 32 disposed on the cantilevered probes 30. One or more of thecantilevered probes 30 in the cantilevered probe array 20 have probeheaters 36 to locally heat selected cantilevered probes 30.Piezoelectric elements 32 can be configured to detect an explosivematerial 16 adsorbed onto the cantilevered probes 30 when the probeheaters 36 heat the cantilevered probes 30.

In some embodiments, the piezoelectric element 32 also serves as apiezoelectric drive and as a piezoelectric sense mechanism. Thepiezoelectric element 32 can detect the explosive material 16 adsorbedonto one or more of the cantilevered probes 30. One or more selectivecoatings 34 may be applied to one or more of the cantilevered probes 30in the cantilevered probe array 20. An interface circuit 40 may becoupled to the cantilevered probe array 20. The enclosure 60 can have aninlet port 62 to allow ingression of the explosive material 16 into theenclosure 60 and an outlet port 64 to allow egression of the explosivematerial 16 or a byproduct thereof from the enclosure 60. When thecantilevered probe array 20 is exposed to the explosive material 16 andthe interface circuit 40 actuates the cantilevered probe array 20 duringor after heating, one or more of the cantilevered probes 30 in thecantilevered probe array 20 may exhibit a response such as a resonantfrequency shift, a shift in bending, a thermal signature, a recoilresponse such as an impulse followed by ring down, a pyroelectric chargegeneration, an impedance shift, a temperature shift, or a combinationthereof.

The cantilevered probe array 20 may include a plurality of cantileveredprobes 30 that are frequency-differentiated. The plurality ofcantilevered probes 30 in the cantilevered probe array 20 may beelectrically connected to a single pair of cantilevered probe arraydrive pads, and one or more groups of cantilevered probes 30 may beincluded within the enclosure 60.

The handheld system 70 may include a controller 50 in communication withthe interface circuit 40. The controller 50 can be configured to receivea shifted cantilevered probe response and piezoelectric element outputsignals from a set of cantilevered probes 30 in the cantilevered probearray 20. The shifted cantilevered probe responses and the piezoelectricelement output signals can be analyzed and used to determine theconstituency and concentration of the explosive material 16.

The cantilevered probe array 20 may include a reference cantileveredprobe 30 r. The reference cantilevered probe 30 r may provide areference cantilevered probe response when the cantilevered probe array20 is exposed to the explosive material 16 and the target chemicalspecies 12.

The handheld system 70 may include a thermally conductive mesh 58 suchas a copper or metal screen substantially surrounding cantileveredprobes 30, such as to limit the egression of thermal energy from anexothermic reaction when the probe heater heats the cantilevered probe.The handheld system 70 also may include a transport mechanism 66 such asa pump, fan or blower and ductwork or piping for transporting theexplosive material 16 and/or the target chemical species 12 to thecantilevered probe array 20. The handheld system 70 may include aconcentrator 68 such as a compressor or a condenser to concentrate theexplosive material 16 proximal to one or more of the cantilevered probes30 in the cantilevered probe array 20. In some embodiments, one or moreheaters of the concentrator 68 are located near the cantilevered probearray 20 so that the explosive material 16 is concentrated on one ormore of the cantilevered probes 30 when the concentrator 68 is locallyheated to desorb the explosive material collected by the concentrator68.

Command and data entry input devices such as buttons, keypads, orsoftkeys, can be incorporated to allow the selection of functions andoperation of the handheld system 70. Results of measurements can bedisplayed on an output device, such as an LCD, or communicated toanother analysis system through a wired communication port such as auniversal serial bus (USB) port or through a wireless communicationprotocol.

FIG. 11 is a flow chart of a method for detecting an explosive material,in accordance with some embodiments of the present invention. Thechemical detection method can include various steps to detect andidentify one or more explosive materials and/or target chemical species,such as with a self-sensed cantilevered probe array that includes apiezoelectric element disposed on one or more cantilevered probes in thecantilevered probe array.

The cantilevered probes in the cantilevered probe array may befrequency-differentiated, separated in the frequency domain such thatany one of the cantilevered probes can be measured independently of theothers using, for example, a frequency generator, a frequencysynthesizer, a controlled oscillator, or an impedance analyzer when thecantilevered probes are configured in series or in parallel with othercantilevered probes. The cantilevered probe array includes, for example,at least two-series connected cantilevered probes electrically connectedto a pair of cantilevered probe array drive pads. Alternatively, thecantilevered probe array may include at least two parallel-connectedcantilevered probes electrically connected to a pair of cantileveredprobe array drive pads. Alternatively, the cantilevered probe array mayinclude a network of series-connected and parallel-connectedcantilevered probes electrically connected to a pair of cantileveredprobe array drive pads. One or more groups of cantilevered probes may beconnected to the same set of cantilevered probe array drive pads or to adifferent set of cantilevered probe array drive pads on the samesubstrate for external connection to an interface circuit.

The cantilevered probe array may include one or more selective coatingsapplied to one or more cantilevered probes in the cantilevered probearray. Exemplary chemical-sensitive coating materials include an epoxyresin, a fluoropolymer, a gold layer, a palladium layer, analcohol-absorbent polymer, a water-absorbent material, achemical-sensitive polymer, a chemical-sensitive layer, a biosensitivematerial, a thiol, and derivatives and combinations thereof. Theselective coating can be applied, for example, by standard depositiontechniques such as sputter depositions, electron beam depositions, orplasma-enhanced chemical vapor depositions, or by dipping, spraying ordispensing the coating material onto at least a portion of one or morecantilevered probes. In another example, a chemical-sensitive selectivecoating is applied to one or more cantilevered probes with a stencilmask and the selective masking of one or more cantilevered probes. Asingle material may be applied through the mask.

A plurality of chemical-sensitive coating materials may be applied to aset of cantilevered probes in the cantilevered probe array. For example,multiple masks may be used for multiple coatings with different coatingmaterials on selected portions of one or more cantilevered probes.Alternatively, coating with multiple materials through a single mask maybe accomplished by spraying a non-homogenous coating material onto a setof cantilevered probes in the cantilevered probe array such thatcantilevered probes in the array are coated with differences in coatingconstituency, thickness, or fraction of coverage.

A probe heater on or near the cantilevered probe can be thermallycoupled to at least one cantilevered probe, which may be heated toinitialize the cantilevered probe prior to exposing it to the explosivematerial or to initiate an exothermal reaction. For example, the probeheater can be used to locally heat the cantilevered probe to an elevatedtemperature to evaporate, burn off, or otherwise remove material fromthe surfaces of the cantilevered probe.

The cantilevered probe array may be initialized, as seen at block 100.Initialization of the array can be accomplished, for example, by runninga scan through the resonant frequencies of the cantilevered probes inthe cantilevered probe array to establish a baseline or to ensure thatall the cantilevered probes and the interface electronics arefunctioning properly.

Explosive material can be exposed to and adsorbed onto one or morecantilevered probes, as seen at block 102. For example, the self-sensedcantilevered probe array can be exposed to an explosive material. Avalve and associated piping may be used to expose the cantilevered probearray to the explosive material and a carrier. The explosive materialmay be transported to the cantilevered probe array using, for example,fans, blowers, or pumps to force flow of the explosive material and acarrier gas or liquid onto the cantilevered probe array. Convectiveprocesses or normal diffusive processes due to concentration gradientsmay be used, for example, to transport the explosive material to thecantilevered probe array for detection.

An explosive material, such as 2,4,6-trinitrotoluene (TNT),2,4,6,n-tetranitro-n-methylaniline (Tetryl),1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), pentaerythritoltetranitrate (PETN), glycerol trinitrate (nitroglycerin), ethyleneglycol dinitrate (EGDN) or derivatives or combination thereof, can beadsorbed onto one or more cantilevered probes in the cantilevered probearray.

The explosive material may be concentrated near or on the cantileveredprobe array. Concentration of the explosive material may beaccomplished, for example, with a compressor and a valve system toincrease the pressure in the vicinity of the cantilevered probe array. Acondenser and a heater may be used, for example, to collect samples ofthe explosive material and then release the explosive material inproximity to the cantilevered probe array. In some embodiments, aconcentrator with one or more heating elements surrounding acantilevered probe array is heated locally after an explosive materialis adsorbed thereon, increasing the concentration of explosive materialin the vicinity of the cantilevered probes and allowing a higheradsorption rate of explosive material onto one or more of thecantilevered probes.

The cantilevered probe can be heated to cause, for example, anexothermic reaction or a phase change with the adsorbed explosivematerial, as seen at block 104. The probe heaters coupled to one or morecantilevered probes may be heated to react the explosive material. Thepiezoelectric element may generate a piezoelectric element output signalwhen the explosive material is reacted. Alternatively, the reaction ofthe explosive material can result in the volatile material beingdesorbed from a cantilevered probe, which causes a shift in the resonantfrequency of the cantilevered probe due to its decreased mass.Alternatively, the reaction of the explosive material may result in aformation of a material on the surface of the cantilevered probe thatincreases the vibrational stiffness of the cantilevered probe andproduces a frequency shift. Alternatively, reaction of the explosivematerial may result in a stressed film on the surface of thecantilevered probe that causes a static deflection of the cantileveredprobe. The static deflection can be measured, for example, with atapping mode where the cantilevered probe is tapped against a referencesurface at a fixed distance away from the cantilevered probe, or with atapping mode where the cantilevered probe is tapped against anadjustable mechanical stop that is adjusted so the cantilevered probehas a consistent amount of contact with the mechanical stop.Alternatively, recoil of the cantilevered probe when the adsorbedexplosive material is ignited or deflagrated may produce an impulseresponse with a ring-down characteristic to identify the event.

A piezoelectric element output signal can be detected, as seen at block106. The piezoelectric element output signal generated by thepiezoelectric element can be detected, for example, with ananalog-to-digital converter or a threshold detector. To validate themeasurement, additional cantilevered probe responses may be detected. Acantilevered probe response may be detected, for example, from at leastone self-sensed cantilevered probe in the cantilevered probe array byactuating one or more cantilevered probes.

In some embodiments, an exposed cantilevered probe array is actuated byapplying an excitation voltage to a piezoelectric material disposed oneach cantilevered probe in the cantilevered probe array. The exposedcantilevered probe array can be actuated with a signal generator or afrequency generator by scanning the cantilevered probes through apredetermined frequency range, allowing the resonant frequencies of oneor more cantilevered probes to be determined. In another example, theexposed cantilevered probe array is actuated by driving the exposedarray at a resonant frequency of one cantilevered probe in thecantilevered probe array, then switching as desired to a resonantfrequency of another cantilevered probe for additional measurements. Inanother example, the exposed cantilevered probe array is actuated bydriving the exposed array at a predetermined frequency, wherein thepredetermined frequency is off-resonance with respect to at least onecantilevered probe in the cantilevered probe array. In another example,the amplitude of vibration is controlled as the cantilevered probestrikes against a fixed or adjustable mechanical stop. In anotherexample, the exposed cantilevered array is actuated with an electricalimpulse applied to the cantilevered probe array.

The piezoelectric element output signal can be analyzed, as seen atblock 108. Analyzing the piezoelectric element output signals and thecantilevered probe response from one or more actuated cantileveredprobes comprises, for example, measuring a shifted resonant frequency, ashifted Q factor, a shifted impedance, a shifted phase, a shifteddeflection amplitude, or a combination thereof and comparing theresponses to known or calibrated responses. A fast Fourier transform(FFT) may be performed on the cantilevered probe responses from one ormore actuated cantilevered probes. The entire array of cantileveredprobes, a subset thereof, or an individual cantilevered probe may beaddressed by selective actuation and detection. With the availability ofa reference cantilevered probe, a reference cantilevered probe responsemay be detected from one or more reference cantilevered probes in thecantilevered probe array. The explosive material may be determined basedon comparing a measured shift from one or more actuated cantileveredprobes to a reference set of cantilevered probe responses, anddetermining the explosive material based on the reference set ofcantilevered probe responses.

The explosive material can be determined, for example, based on thepiezoelectric element output signal from a piezoelectric elementdisposed on the cantilevered probe, as seen at block 110. Alternativelyor in addition to, a non-explosive material may be adsorbed onto thesurface of the cantilevered probe and determined. Determining theexplosive material, non-explosive material or other target chemicalspecies may include, for example, analyzing the piezoelectric elementoutput signal and other cantilevered probe responses such as a resonantfrequency shift of the cantilevered probe, a shift in bending of thecantilevered probe, a thermal signature, a recoil response, apyroelectric charge generation, an impedance shift, a temperature shift,or a combination thereof.

To determine the explosive material or other target chemical species,the self-sensed cantilevered probe array may be scanned through apredetermined frequency range. When activated, for example, with aninterface circuit that scans through the resonant frequencies of one ormore cantilevered probes, each cantilevered probe, in turn, may beexcited and oscillated by the interface circuit as the frequency of theoscillator or frequency generator is scanned through each resonantfrequency. Depending on the type and amount of a explosive material andthe coating on the cantilevered probe, the cantilevered probes in thearray may exhibit shifted cantilevered probe responses such as a shiftedresonant frequency, a shifted Q factor, a shifted impedance, a shiftedphase, a shifted deflection amplitude, or a combination thereof.

Temperature measurements from one or more probe heaters serving as atemperature sensor or other on-board temperature sensors may be used toindicate the temperature of the heated cantilevered probe, from whichthe ignition temperature of the explosive material can be determined.Characteristic properties such as the heat of vaporization, meltingtemperature, phase change, chemical reactions, exothermic reactions, orendothermic reactions associated with adsorbed explosive material andother target chemical species may be interpreted to aid in thedetermination of the explosive material or target chemical species.

A controller or a software application running on a computer or digitaldevice may be used to analyze the cantilevered probe responses anddetermine one or more components and their concentration in the sample.The explosive material may be determined in part based on the detectedreference cantilevered probe response, for example, by a common modecorrecting for effects such as temperature, pressure and viscosity ofthe sampled medium. The detected explosive material or target chemicalspecies may include, for example, mercury, hydrogen, an alcohol, watervapor, a chemical element, a chemical compound, an organic material, aninorganic material, a gaseous substance, a liquid, a biologicalmaterial, a DNA strand, a bioactive agent, a toxin, and derivatives andcombinations thereof.

Using pattern recognition, modeling functions or signal processingtechniques such as fuzzy logic, the explosive material may be determinedbased on comparing a measured shift from one or more actuatedcantilevered probes to a reference set of cantilevered probe responses,and determining the explosive material based on the reference set ofcantilevered probe responses. The reference set of cantilevered proberesponses may comprise, for example, a learned set from calibration runsor from a statistical database with expectation values for variousexplosive materials and target chemical species.

Having illustrated and described the principles of the invention inexemplary embodiments, it should be apparent to those skilled in the artthat the illustrative embodiments can be modified in arrangement anddetail without departing from such principles. In view of the manypossible embodiments to which the principles of the invention can beapplied, it should be understood that the illustrative embodiments areintended to teach these principles and are not intended to be alimitation on the scope of the invention. We therefore claim as ourinvention all that comes within the scope and spirit of the followingclaims and their equivalents.

1-26. (canceled)
 27. A system for detecting a target material, thesystem comprising: means for adsorbing a target material onto acantilevered probe; means for heating the cantilevered probe; and meansfor identifying the target material based on a piezoelectric elementoutput signal.
 28. A method for detecting a target material, comprising:exposing a cantilevered probe to a carrier comprising a target materialsuch that the target material is transferred onto the cantileveredprobe; heating the cantilevered probe; and piezoelectrically detecting amovement of the cantilevered probe or a property of the cantileveredprobe.
 29. The method of claim 28, wherein the target material is anexplosive material.
 30. The method of claim 28, wherein heating thecantilevered probe comprises heating the cantilevered probe to atemperature sufficient to cause the target material to undergo a phasechange.
 31. The method of claim 28, wherein heating the cantileveredprobe comprises heating the cantilevered probe to a temperaturesufficient to cause the target material to deflagrate or ignite.
 32. Themethod of claim 28, wherein piezoelectrically detecting the movement ofthe cantilevered probe or the property of the cantilevered probecomprises generating an electrical signal in response to the movement ofthe cantilevered probe or the property of the cantilevered probe with apiezoelectric element connected to the cantilevered probe.
 33. Themethod of claim 28, wherein transferring the target material onto thecantilevered probe causes the movement of the cantilevered probe or achange in the property of the cantilevered probe.
 34. The method ofclaim 28, further comprising piezoelectrically actuating a movement ofthe cantilevered probe.
 35. The method of claim 34, whereinpiezoelectrically detecting and piezoelectrically actuating areperformed by the same piezoelectric element.
 36. The method of claim 34,wherein the cantilevered probe is frequency-differentiated from othercantilevered probes in a cantilevered probe array and piezoelectricallyactuating the movement of the cantilevered probe comprises applying avariable-frequency drive voltage.
 37. The method of claim 28, furthercomprising causing the target material to undergo a phase change or areaction, wherein the phase change or the reaction causes the movementof the cantilevered probe or a change in the property of thecantilevered probe.
 38. The method of claim 28, wherein the cantileveredprobe undergoes a resonant frequency shift, and piezoelectricallydetecting the movement of the cantilevered probe or the property of thecantilevered probe comprises detecting the resonant frequency shift. 39.The method of claim 28, wherein the cantilevered probe undergoes animpedance shift, and piezoelectrically detecting the movement of thecantilevered probe or the property of the cantilevered probe comprisesdetecting the impedance shift.
 40. The method of claim 28, wherein thecantilevered probe undergoes a temperature shift, and piezoelectricallydetecting the movement of the cantilevered probe or the property of thecantilevered probe comprises detecting the temperature shift.
 41. Themethod of claim 28, further comprising identifying the target materialbased on the movement of the cantilevered probe or a change in theproperty of the cantilevered probe.
 42. The method of claim 28, furthercomprising comparing a cantilevered probe response to a referencecantilevered probe response.
 43. A method for making a chemicaldetection system, comprising: forming a cantilevered probe having aprobe heater thermally coupled to the cantilevered probe and having apiezoelectric element disposed on the cantilevered probe.
 44. The methodof claim 43, wherein forming the cantilevered probe comprises depositinga piezoelectric film on a surface of the cantilevered probe.
 45. Themethod of claim 43, further comprising depositing a selective coating ona surface of the cantilevered probe.
 46. The method of claim 43, furthercomprising fabricating the cantilevered probe with other cantileveredprobes to form a cantilevered probe array.